1. Field of the Invention
The present invention relates to an input stage for a Low-Voltage Differential Signal (LYDS) receiver circuit. More particularly, this invention relates to a comparator in the receiver circuit. Still more particularly, this invention relates to a high-speed comparator that does level shifting in the input stage.
2. The Prior Art
Most electronic devices used in today's society are made up of many different integrated circuits. The integrated circuits in these devices are becoming denser as the dimensions of semiconductors components of the integrated circuits decrease. The decreased dimensions of the semiconductor components allow for faster devices that do not require as much power or electrical current to operate. For example, many conventional semiconductor components used to require 3.3 volts of power to operate. However, other semiconductor components, such as transistors require approximately 1.2 volts to operate. The use of components having lower power requirements is important in mobile devices such as laptop computers and cellular telephones. The lower power allows a power supply in the device, such as a battery, to last longer and be simaller.
It is a problem that many devices still incorporate integrated circuits with high-powered components and integrated circuits with the lower-powered components. These devices may connect the lower power integrated circuits to high-powered integrated circuits. Thus, an integrated circuit operating on a lower voltage may receive an input at a higher voltage. This is a particular problem when an input of a higher voltage from a high voltage integrated circuit is applied to the lower voltage integrated circuit.
The particular problem is that the thin film oxide of the low voltage integrated circuit may suffer oxide breakdown from exposure to a voltage higher than the maximum supply voltage. This will cause catastrophic damage to the components of the low voltage integrated circuit.
One area where this is a particular problem is LVDS circuits that provide I/O communication to Integrated circuit. Typically, an LVDS receiver operates at 1.2 volts. However, circuitry connected to the LVDS receiver may operate at 3.3 volts.
Thus, there is a need in the art for an input stage of a low-powered LVDS receiver circuit that limits the voltage of signals applied to the circuit.